1. Field of the Invention
The present invention relates to an optical information recording/reproducing device which optically records and reproduces information on an optical recording medium such as an optical card, and an optical head used in the optical information recording/reproducing device, and more particularly to an optical information recording/reproducing device including a first light source for producing an information recording optical beam and a second light source for producing an information reproducing optical beam, and an optical head used in the optical information recording/reproducing device.
2. Related Art Statement
An optical recording medium such as an optical card or the like includes a plurality of tracks extending in parallel to each other. Meanwhile an optical information recording/reproducing device for the optical card has an optical head for optically recording/reproducing information to/from the optical card. In order to perform an information recording/reproducing, the optical recording medium and the optical card reciprocate in the track direction of the optical recording medium and in a direction extending perpendicularly thereto.
Such an optical information recording/reproducing device is disclosed, for example, in Japanese Laid-open Patent No. HEI 2-61830. The optical information recording/reproducing device provided with a plurality of light sources is provided, independently from each other, with the plurality of light sources, an optical beam producing light source for generating information recording optical beam and a light source for generating information reproducing light beam so that so-called verify operation can be performed simultaneously with scanning for recording, which causes an information reproducing optical beam to record the information onto an optical recording medium, and the quality of the recording by reproduction of the information by the information reproducing optical beam.
In the optical information recording/reproducing device, the effective recording speed is substantially doubled as compared with an arrangement in which, in a single light-source type device, an optical beam spot is scanned twice on a track formed on an optical recording medium, upon performing verification.
Further, since a two-light source type device can maintain an amount of light emission from the information reproducing light source constant, a focus servo signal and a tracking servo signal can be obtained from an optical beam for information reproduction. Hence the two-light source type device has an advantage in that a stable servo control can be performed even during recording of the information.
FIG. 10 is a view showing an arrangement of an optical head built in the conventional two-light source type optical information recording/reproducing device. A recording optical beam generated by a semiconductor laser 101 is converted into a nearly oval, parallel beam by a collimator lens 102. Moreover, a shaping prism 103 reduces only the major axis component of the oval form of the parallel beam so as to be shaped into a nearly round beam. Subsequently, a round iris 104 further stops down the beam diameter, of the parallel beam such that the spot size on the recording medium is brought to predetermined dimension, and the parallel beam is incident upon a polarizing beam splitter 105. Since the recording round beam is formed of nearly a S-polarized component because of the property of the semiconductor laser 101, most of the beam is reflected from a reflecting surface of the polarizing beam splitter 105 and is incident upon the optical axis of an objective lens 106. The light is condensed by the objective lens 106 to form a round spot on an optical card 107 and to enhance locally the energy density so that a thermal irreversible change is generated in the recording layer of the optical card 107 to form a recording pit.
Meanwhile, a single-surface light emitting diode 108 having a light emitting surface in the form of a slit, for example, is used as a light source of the reproducing optical beam. The optical beam for reproduction generated from the reproducing light emitting diode 108 is converted to a nearly parallel beam by the collimate lens 109 and is incident upon polarizing beam splitter 105. The polarizing beam splitter 105 penetrates only the P-polarizing component thereof. The component is incident upon a position shifted from the optical axis with respect to the objective lens 106 to form on the optical card 107 an image projected on the light emitting surface of the light emitting diode 108.
FIG. 11 is a view showing the positional relationship between an optical spot 123 of the recording optical beam from the semiconductor laser 101 formed on the optical card 107 and the reproducing optical beam spot 124 from the light emitting diode 108. A plurality of guide tracks 121 are formed in parallel with each other and extend longitudinally on the optical card 107. Information tracks 120 are formed between the guide tracks 121. The optical beam spots 123 and 124 are formed so as to move relatively in the direction indicated by the arrow a or b in parallel to the extending direction of the track with respect to the optical card 107. The semiconductor laser 101 receives pulses modulated by information to be recorded and emits light in accordance with the pulses. Pits 122 are formed sequentially on the optical card 107 to record information in a pit chain form on the information track 120, as shown in FIG. 11. The relative distance between the reproducing optical beam spot 124 and the recording optical beam spot 123 is adjusted by providing a relative angle difference between the optical axis of the reproducing optical beam and the optical axis of the recording optical beam before being incident upon the objective lens 106 upon assembling and adjustment of an optical head.
The information reproducing optical beam emitted from the light emitting diode 108 is brought to a condition in which a light amount modulation is applied to the optical beam, depending upon presence or absence of the guide tracks 121 and the pits 122 on the optical card 107 and is reflected regularly back from the optical card 107. The reflective beam passes reversely through the objective lens 106 and is converted to nearly parallel beam light so as to be introduced to the polarizing beam splitter 105 (see FIG. 10). The parallel light maintains substantially its P-polarization because it is reflected regularly back from the optical card 107 and most of the component passes through the polarizing beam splitter 105 and is introduced to the reflective mirror 114. The light reflected by a reflective mirror 114 is condensed by a condensing lens 115 and is further split by a half-mirror lens 116. The light is incident upon an optical detector 117 for signal reproduction and tracking and an optical detector 118 for focusing. As described above, the optical beam for reproduction is incident upon a position eccentric from the optical axis with respect to the objective lens 106 so that detection of a focus error is performed by a so-called out-of axis type. The arrangement is such that a twice-divided light receiving element, for example, is arranged at the focusing optical detector 118 to detect a shift or movement in an image of a reproducing light beam spot 114 due to a focus deviation.
FIG. 12 is a view showing a recording optical beam spot image 123a and the reproducing optical beam spot image 124 projected on the signal reproducing and tracking optical detector 117. Signal reproducing light receiving elements 132, and 133, and tracking light receiving elements 130 and 131 are arranged on the optical detector 117. In FIG. 11, the image 124a in which the reproducing optical beam spot is enlarged and projected is imaged at a proper position on the light receiving elements under a condition in which there are no track deviation and no focus deviation. The tracking light receiving elements 130 and 131 detect a positional variation in a track guide image caused by a track deviation as a change in light receiving amount to produce a tracking error signal. Moreover, upon reproduction of a signal, the signal reproducing light receiving elements 132 and 133 detect the presence or absence of pits in two tracks to output a reproducing signal.
Upon recording of information, when the optical card 107, as shown in FIG. 12, moves in the direction indicated by the arrow a, the pit 122 formed by the recording optical beam spot 123 moves in the direction of the optical image 124 of a reproducing optical beam. Accordingly, when the pit 122 reaches the position of the optical image 124, a change in light amount occurs in the signal reproducing light receiving element 133 on the optical detector 117. The signal reproducing light receiving element 113 detects the change in light amount to output a reproducing signal. That is, when the optical memory card 107 moves in the direction of the arrow a, a so-called verify operation can be performed in which a reproducing signal is obtained immediately after information has been recorded. On the other hand, when the optical card 107 moves in the direction of the arrow b, the recorded last pit line is detected and, subsequently, an additional recording operation can be performed.
In connection with the above, since spacing between a recording beam and a verify beam and the relative velocity between the recording beam and the card pick-up (may be actually measured, or a control target value may be utilized) is previously known, the delay time from a recording beam irradiation to production of a verify signal and delay time from detection of the last pit line to start of the postscript operation can be operated or computed. In view thereof, regarding the start timing of the verify operation, and the start timing of the postscript or additional operation, only computing time decided by the above-described method is measured and is decided by a timer.
However, in such conventional two-light source type optical information recording/reproducing device, as will be clear from FIG. 12, the light image 124 of the reproducing optical beam is formed only at a single location with respect to the recording optical beam spot 123. Accordingly, in a case where an optical recording medium moves in a fixed direction or in the direction indicated by the arrow a in the aforesaid example, a verify operation can be performed immediately after recording. However, there is a disadvantage in that, in a case where the moving direction of the optical recording medium is reversed and moves in the direction indicated by the arrow b, a reproducing signal cannot immediately after recording be obtained.
Furthermore, there is a disadvantage in that, although when the optical card moves in the direction of the arrow b, a reproduction signal can be obtained in advance, when the optical card moves in the direction of the arrow a, the additional recording operation cannot be performed.